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In a systemic review, MacDonald et al.15concluded that there was a strong negative relationship between higher BMI and serum testosterone levels. 2Full size imageAssociation between the WWI and testosterone deficiency using a restricted cubic spline regression model. The WWI was calculated as waist circumference (cm) over the square root of weight (kg), and a total testosterone level of less than 300 ng/dL was defined as testosterone deficiency. The lowest levels of total and free testosterone were observed in men with relatively high WC despite relatively low overall obesity (BMI), suggesting that WC should be the preferred anthropometric measurement in predicting endogenous testosterone levels.
Overall for each unit increase in BMI, there was a 2% fall in TT and cFT, and for each 10 cm increment in WC, TT and cFT levels declined by 7%. While multivariate analyses in large population derived cross-sectional studies allow adjustment for potential confounding factors, such adjustment may not be adequate when there are complex relationships between multiple factors or if there is a subgroup within the population in which the behaviour is divergent from the group as a whole. Age was not a significant univariate predictor of TT and remained nonsignificant after including either BMI or WC in the models (results not shown). SHBG was not correlated with cFT on univariate analysis and the inclusion of SHBG in multivariate models of cFT did not add to the prediction of cFT (results not shown). There was no improvement in the prediction of SHBG when Ht was added to either WC or the combination of age and WC. The scatter plots showing the correlations of TT, cFT, SHBG and LH with age are shown in Figure 1. WC and Ht were independent predictors of TT when included together and there was an increase in the regression coefficients of both variables when they were combined, with the contribution of Ht becoming significant.
Given the relationship between adipose tissue and testosterone levels, WWI may be a more detailed reflection of the association between obesity and TD, and our study demonstrated a close association between WWI and TD. Firstly, the fully adjusted linear regression analysis results showed that each unit increase in BMI, WC, and weight corresponded to decreases in total testosterone levels of -7.79 (-10.49, -5.09), -3.74 (-4.53, -2.95), and − 1.82 (-2.40, -1.24), respectively. Smooth curve fitting and generalized additive models were employed to investigate whether there was a linear relationship between WWI and total testosterone levels, as well as the prevalence of TD.
In this study, we have examined the relationships of ageing, adiposity and testosterone levels in a highly select group of ageing men (over the age of 54 years) who were recruited on the basis of having symptoms consistent with hypoandrogenism but who were non-smokers and otherwise in good health. Height (Ht), weight and waist circumference (WC) were measured, and body mass index (BMI) and waist-to-height (WHt) ratio were calculated. To examine the relationship of total and free testosterone and sex hormone-binding globulin (SHBG) with central obesity in men, we studied 1548 men aged 25–84 years that took part in the 1994–1995 survey of the Tromsø study.
Previous studies have explored the relationship between body mass index (BMI) and testosterone levels, indicating that obese individuals tend to have lower testosterone levels . This investigation firstly unveiled a negative linear association between WWI and total testosterone levels, coupled with a positive linear relationship with the prevalence of TD in U.S. male adults aged 20 years and older. Weighted multivariable linear regression and logistic regression analyses were employed to investigate the relationships between WWI and total testosterone levels, and the risk of TD, respectively. The correlation between the WWI and testosterone levels might be explained by the fact that the WWI is an obesity index and reflects abdominal fat mass28. Our study was in line with previous studies and revealed a negative relationship between the WWI and serum total testosterone levels and a positive relationship with testosterone deficiency, which remained robust after adjusting for other confounders. Esmaeili etal.23reported that the hip circumference, waist circumference, waist-to-hip ratio, and waist-to-height ratio were negatively related to serum testosterone levels.
All sex steroid hormones were measured at Boston Children’s Hospital (Boston, MA, USA) by laboratory technicians blinded to participant characteristics. Finally, measurements were taken at the end of the individual’s normal expiration. The anthropometry examinations of WC and weight were conducted in mobile examination center by trained health technicians under controlled conditions. A total of 4099 participants were included after further exclusion of men who were taking sex hormone medication or had incomplete data on potential covariates. The NHANES study protocols were reviewed and approved by the Research Ethics Review Board of the NCHS, and all survey participants provided the written informed consent. A sophisticated multistage probability design was employed to obtain a nationally representative sample of non-institutionalized United States residents.

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